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CHAPTER VI.
MARKING-OFF, MACHINING, FITTING, AND ERECTING.

WHEN an engine or machine is first projected, a rough
'general* drawing is made by the draughtsman, in order to
determine the relation of the several parts; after which the
6 detailing' takes place, which consists in drawing out each piece
separately to a large scale, and at the same time classifying the
work—putting all the forgings upon one set of sheets, and the
castings upon others—so as to facilitate the distribution of the
parts to the various shops and avoid delay.

Detail Drawings are fully provided with dimensions, and
have red lines drawn round surfaces that need Fitting or Machining,
viz., such as are required to fit or work together; and the Pattern
Maker and Smith are thus enabled to decide where to leave extra
material. It is the business of the Marker-off to ' line out' the
rough work received from the above men; that is, indicate by a
boundary line the amount of material to be removed by the
Fitter or Machinist. The work is then finished and passed on
to the Erector, who carefully puts it together to form the com-
pleted machine.

The Marker-off's Tools.—A large plane table or
Surface flate is first required. This is shewn in Fig. 191, and
its size varies with the average work to be lined-out upon it—
from 4 ft. by 2 ft. up to 12 ft. by 4 ft. It is well ribbed under-
neath to prevent any possible distortion, and is planed very truly,
being better also if filed up and a little scraping done upon it.
The edges should be planed truly and adjacently at right angles,
sd that squares may be applied to them when necessary. Lastly,
the feet should stand upon a firm bed of concrete, and be
adjusted until the surface of the table is truly level, which often
assists the marking-off considerably.

V blocks, to support cylindrical work upon the table, are